Dry chemical extinguishing systems

This section applies only to fixed extinguishing systems that use dry chemical as the extinguishing agent and are installed to meet a particular OSHA standard; those systems must also comply with 1910.160.

• See the scope at 1910.161(a).
• Employers should confirm the particular OSHA standard that requires the fixed system and then apply both 1910.161 and the general fixed-system rules in 1910.160.

Yes — the employer must assure the dry chemical agents are compatible with any foams or wetting agents used together.

• The requirement is in 1910.161(b)(1).
• Practical steps include obtaining manufacturer compatibility data, written confirmation from the agent suppliers, or lab testing before storage or discharge, and keeping that documentation with your system records.

No — the employer may not mix together dry chemical agents of different compositions in the same system.

• 1910.161(b)(2) requires refilling only with the chemical stated on the approval nameplate or an equivalent compatible material.
• To comply: tag cylinders with the approved agent, use only the manufacturer-approved replacement, and keep supplier documentation that shows equivalence and compatibility.

A pre-discharge employee alarm is required whenever dry chemical discharge may obscure vision so employees have time to safely exit the discharge area before the system discharges.

• The requirement is in 1910.161(b)(3).
• The alarm must comply with 1910.165 (the employee alarm standard) to ensure appropriate audibility/visibility and sufficient warning time for evacuation.

Compliance means providing an alarm system that meets the employee alarm rules in 1910.165 and that gives workers enough time to leave the area before a dry chemical discharge that would obscure vision.

• Design the alarm so it is heard/seen where employees work, test it regularly, and document tests and any drills.
• Use the performance principles of 1910.165 for audibility, visibility, and notification methods; tailor evacuation time to your facility layout and employee mobility.

You must sample the dry chemical supply at least annually for all systems except stored-pressure systems to ensure the chemical is free of moisture that could cause caking or lumps.

• See the sampling requirement at 1910.161(b)(4).
• Practical steps: establish an annual sampling schedule, follow manufacturer-recommended sampling methods, and keep records of sampling results and corrective actions.

No — the annual sampling requirement does not apply to stored-pressure systems; it applies to all dry chemical supplies except stored-pressure systems.

• The exclusion is explicit in 1910.161(b)(4).
• For stored-pressure systems, follow the manufacturer's maintenance guidance and any other applicable requirements in 1910.160.

The system must reach its designed concentration within 30 seconds of initial discharge.

• This performance requirement is stated in 1910.161(b)(5).
• Verify compliance by using the system design data (nozzle sizes, flow rates, agent quantity), manufacturer test reports, or system commissioning tests; adjust layout or agent storage if tests show the concentration is not reached in 30 seconds.

An "equivalent compatible material" is a dry chemical that is compatible with the system and the original agent identified on the approval nameplate and acceptable to the system approval/manufacturer.

• The rule is in 1910.161(b)(2).
• Employers should keep the approval nameplate, get written confirmation from the system or agent manufacturer that the substitute is compatible, and retain that documentation as evidence of compliance.

You must provide a pre-discharge alarm that complies with 1910.165 and gives employees time to safely exit the discharge area before the system discharges.

• See 1910.161(b)(3).
• In practice: create evacuation procedures, conduct drills, post clear exit routes, and ensure the alarm reaches all affected employees with adequate lead time.

While 1910.161(b)(4) requires annual sampling, it does not specify a record retention period; employers should document sampling dates, methods, results, and corrective actions to demonstrate compliance.

• The sampling mandate is at 1910.161(b)(4).
• Maintain written or electronic logs, supplier test reports, and disposal/replacement records so you can show inspectors that sampling was performed and any moisture issues were addressed.

Systems covered by 1910.161 must meet the dry-chemical-specific rules in 1910.161 and also comply with the general fixed extinguishing system requirements in 1910.160.

• See the cross-reference at 1910.161(a).
• Review 1910.160 for additional design, installation, inspection, and maintenance obligations that apply to all fixed systems; combine the two sections when creating your written procedures and maintenance schedules.

Employers should follow the annual sampling requirement in 1910.161(b)(4), store chemicals in dry, secure containers, protect them from humidity, and follow manufacturer storage instructions to prevent moisture-caused caking.

• Implement a labeled inventory, rotate stock, inspect containers for seals and moisture intrusion, and perform corrective action (drying or replacement) when samples show moisture or lumping.

If the approval nameplate is missing or unreadable, you must determine the original approved chemical and obtain the manufacturer's or approval agency's written guidance before refilling; do not mix unknown agents.

• The underlying rule is 1910.161(b)(2).
• Steps: contact the system manufacturer or the approval agency for identification, document their guidance, and only refill with the identified chemical or a documented compatible equivalent.